Conventionally, in order to form fine electrodes and circuits of electronic parts and so forth, it is known that a conductive ink containing fine silver particles (silver nanoparticles) having particle diameters of a few nanometers to tens nanometers dispersed in a dispersing medium, or a conductive paste made into a paste after mixing silver nanoparticles with a binder resin and a solvent, is applied on a substrate, and then, heated at a low temperature of about 100 to 200° C. to be burned to sinter the fine silver particles with each other to form a silver conductive film.
Such fine silver particles for use in conductive inks and conductive pastes have a very high activity and are easy to proceed the sintering thereof even at a low temperature, so that they are unstable particles as they are. For that reason, in order to prevent the sintering and aggregation of fine silver particles with each other to ensure the independence and preservation stability of the fine silver particles, it is known that fine silver particles coated with an organic protective material of an organic compound are dispersed in a dispersing medium to be preserved as a fine silver particle dispersing solution.
As fine silver particles which are coated with an organic protective material and which can be used for such a fine silver particle dispersing solution, there are proposed silver particles which have an average particle diameter of 3 to 20 nm and which are coated with an organic protective material of a primary amine having a carbon number of 6 to 12 (see, e.g., Japanese Patent Laid-Open No. 2009-138242).
However, the fine silver particles coated with an organic protective material, such as a primary amine, as proposed in Japanese Patent Laid-Open No. 2009-138242, are hydrophobic, so that they are aggregated in a polar solvent to have a bad dispersion therein. For that reason, there is a problem in that the viscosity of a fine silver particle dispersing solution containing such fine silver particles dispersed in a polar solvent is increased, so that the resistance of a silver conductive film is increased if such a fine silver particle dispersing solution is used for producing the silver conductive film. On the other hand, the fine silver particles coated with such an organic protective material have a good dispersion stability in a nonpolar solvent. However, if the fine silver particle dispersing solution containing the fine silver particles dispersed in a nonpolar solvent, together with a resin binder, is used for producing a conductive paste, there is a problem in that the nonpolar solvent generally has a bad compatibility with the resin binder, so that it is not possible to dissolve the resin binder therein.